The present invention relates to the alarm buzzer which is to be attached to a printed circuit board and operates to generate a warning buzzer sound upon emergencies such as fire and gas leakage.
Various types of alarming devices have been developed to prevent casualty due to fire and gas leakage. For example, some types of the alarming devices which are known to operate with an alarm signal which is generated by amplifying a variation of weak current which is detected when a smoke or gas passes through an air which is ionized by a weak radioactive ray and supplied with the weak current, or utilize a light instead of the radioactive ray. These types of alarming devices employ the printed circuit boards B' on which electronic parts which detect smoke or gas and amplify the current are mounted with the alarm buzzer A'. (See FIG. 1). The alarm buzzer A' comprises, as shown in FIG. 2, the electromagnet 1', yoke 2' to which the electromagnet 1' is attached while being insulated, armature 4' which is connected with the plate spring to the yoke 2' and vibratory plate 5' which are incorporated in the housing 6'. The lead wire 7' of one power line connected to the housing 6' and the lead wire 9' of the other power line connected to one end of the coil 8' of the electromagnet 1' are attached to the printed circuit board 3'. When the power supply is connected to the lead wires 7' and 9', the current passes through the lead wire 9' to the coil 8' and through the plate spring 3', armature 4', vibratory plate 5', housing 6' to the lead wire 7'. Then the electromagnet is energized to attract the armature 4' and consequently the contacts 4a' and 5a' of the armature 4' and the vibratory plate 5' is electrically disconnected to de-energize the electromagnet 1'. The above procedure of the operation is repeated to vibrate the vibratory plate 5' and the alarm buzzer sound is generated. The counter electromotive force is generated by the coil 8' the instant the contact 4a' of the armature 4' and the contact 5a' of the vibratory plate 5' are disconnected and the spark is produced between the contacts 4a' and 5a'. At the same time, a high voltage is applied to the power supply circuit and therefore the contacts 4a' and 5a' are melted and damaged on their surfaces. For this reason, the lead wire 10' is connected to the plate spring 3' to prevent such damage.
Conventional alarm buzzers carry the following various problems.
(1) The yoke 2' is fixed to the base of the housing 6' with rivets and both the yoke 2' and the housing 6' are made of conductive materials. To ensure the insulation, an insulation bush is inserted into the hole provided in the yoke 2' and the rivet should be driven into this insulation bush. Preparation of the insulation bush and insertion of the bush into the hole of the yoke 2' require more efforts than expected.
(2) One end of the iron core of the electromagnet is fixed to the yoke 2' to fix the bobbin 11' of the electromagnet to the yoke 2' and the flange 21' is provided on the other end of the iron core. However, such flange raises the production costs of the iron core and complicates the assembly work of the alarm buzzer.
(3) For attaching the alarm buzzer to the printed circuit board B', the bracket 12' is attached to the bottom of the housing 6' and the bracket 12' is attached to the printed circuit board B' with screws 13'. However, this kind of work for installation also requires a great deal of effort.
(4) The lead wires 7', 9' and 10' are inserted into the holes provided in the printed circuit board B' and soldered to the rear side of the printed circuit board B'. This work is troublesome.
(5) As shown in FIG. 3, the plate spring 3' is attached together with the lug terminal 14' to the yoke 2' and the lead wire 10' is soldered to this lug terminal 14'. This work takes a long period of time.
As described above, the conventional alarm buzzers employ many parts and require troublesome work such as soldering, machining of the iron core, fixing by screws etc., resulting in expensive production costs and causing automation of the manufacturing to be difficult.